The present invention relates to a method of manufacturing an electroconductive antireflection film and a glass faceplate with the antireflection film formed thereon. In detail, it relates to an image display faceplate or a screen in a panel of a CRT, which is applied to on the surface of the glass plate with a film proper to improve the electrically charge-preventive or anti-static characteristics and the electromagnetically shielding characteristics of the surface of a glass plate such as the image display faceplate, and a method of manufacturing the electroconductive polymeric antireflection film.
Recently, a wide use of an anti-explosion type cathode ray tube allows a face cover glass to be unnecessary in a television receiver, a monitor, etc., regarding the prevention of electrostatic charge, thereby exposing the front portion of the cathode ray tube, and giving electric shock by charged electrical high voltage, to the person who comes access to the faceplate of the cathode ray tube. Furthermore, dust in air, particles, etc., are adhered to by the electric force, and accumulated on, the charged faceplate of the cathode ray tube, thereby having the image on the display faceplate difficult to see.
The cause of electrostatic charge as to the faceplate panel as one example of the glass plate is as follows. A thin and uniform aluminium film is deposited by vacuum on the phosphor screen structure on the interior surface of the faceplate panel. When an electric power is applied to, a high anode voltage is applied to the aluminium film. Electric charges generate on the exterior surface wall of the panel by electrostatic induction due to the high voltage of the inside aluminium film.
Electroconductive coatings are used as antistatic layers on display screens of display devices, in particular cathode ray tubes (CRTs). Said layers have a sheet resistance, for example, of 106 to 1010 xcexa9/xe2x96xa1 and are hence sufficiently electroconductive to ensure that a high electrostatic voltage present on the outside surface of the display screen is removed within a few seconds.
However, shielding from electromagnetic radiation is becoming ever more important. Cathode ray tubes, such as display tubes for TVs and monitor tubes, comprise a number of radiation sources which may be hazardous to the user""s health if he is exposed to said sources for a long period of time. A substantial part of the electromagnetic radiation generated can be screened off with metal in a simple manner via the housing of the cathode ray tube. However, radiation emitted via the display screen may substantially add to the amount of radiation to which the user is exposed. This problem is solved by applying a well-conducting coating on the surface of the display screen. Said coating must also be sufficiently transparent in the wavelength range of from 400 to 700 nm, i.e. the transmission must be at least 60%. A well-known material which can be used for a transparent and well-conducting coating is indium-doped tin oxide (ITO). Such a layer can be provided by means of vacuum evaporation or sputtering. Said method requires, however, expensive vacuum equipment. ITO layers can also be manufactured by firing spin-coated or sprayed layers of solutions of indium-tin salts by means of a sol-gel process. Said firing operation should be carried out at a temperature of at least 300xc2x0 C. This temperature is much too high to be used with a complete display tube which, in order to preclude damage to parts of the display tube, can withstand temperatures of maximally 160xc2x0 C., thus this process being improper for such display tube.
Korean patent publication No. 2713 as one prior arts for providing an anti-static characteristics on the image display faceplate describes one such electroconductive coating formed by the steps of preparing a slurry by dispersing indium-doped tin oxide(ITO) into an alcohol solution of alkoxysilane Si(OR)4(R is an alkyl group), spraying the slurry on the faceplate panel, and heat-treating the sprayed panel at a relatively high temperature.
That is, such coating should be also heat-treated at a temperature of at least 300xc2x0 C. in order to obtain sufficient electroconductivivity. However, such coating is improper for a CRT since damage causes in parts of the CRT at a temperatures above 160xc2x0 C. And, to obtain low reflectivity effect, an additional low-reflective silica coating is required on the ITO coating, thereby, making the process for obtaining at least two coating layers complicated.
U.S. Pat. No. 5,742,119 issued to Aben, et al. on Apr. 21, 1998, discloses a display screen of a cathode ray tube provided with electroconductive antireflection coatings of a complicate structure as shown in FIG. 1. In FIG. 1, a cathode ray tube 1 has a glass envelope tube 2 comprising a display panel 3, a funnel 4 and a neck 5. In the neck 5, there is provided one (or three) electron gun(s) 7 for generating an electron beam, and an electroconductive coating 8 is provided on the outer surface of the panel 3, which is connected to the ground 9. On the electroconductive coating 8 is provided with three additional layers consisted of a first additional layer 10 of silicon dioxide, a second additional layer 11 of titanium dioxide and a third additional layer 12 of silicon dioxide.
However, the metallic oxide costs too much, thereby making the manufacturing cost very high. Furthermore, the problem is that while the metallic oxide exists dispersedly in the alcohol solution, deposition problem arises due to cohesion between the particles according the condition of the surroundings, thereby making spots or unevenness and lowering the electroconductivity.
Accordingly, it is one object of the present invention to provide a glass plate such as an image display faceplate having high-electroconductive and antireflective film which can be formed using electroconductive organic polymer in a simple method and at a low cost, and have an improved anti-static characteristic and an electromagnetically shielding characteristic with a strong film hardness and a strong adhesive strength. Also, the present invention provides a method of making such film.
To accomplish the aforementioned purpose, the present invention provides a method of manufacturing an image display glass plate, on the outside surface of which an polymeric electroconductive film is formed as an antistatic layer, the method comprising the steps of: dissolving in alcohol an aqueous solution of organic polymer containing polyethylenedioxythiophene which polystyrenesulphonate is doped to; adding silicon alkoxide to the alcoholic solution for reinforcing adhesion; preparing an organic polymeric electroconductive solution by adding pure water and a basic catalyst for hydrolysis; and applying the electroconductive solution on the image display glass plate, thereby forming the polymeric electroconductive film as an antireflective film.
The applying step is performed by spin-coating said electroconductive solution onto the image display glass plate, and then the polymeric electroconductive film is formed by heat-treating the spin-coated polymeric electroconductive film of the image display glass plate at a temperature of about 150xc2x0 C. Said alcoholic solvent is of 30xcx9c90 wt. % and can be selected from a group consisting of a methanol, an ethanol, an isopropanol, a butanol, and combinations thereof.
In a preferred embodiment, said organic polymeric electroconductive solution contains polyethylenedioxythiophene of 0.03xcx9c0.50 wt. %, which polystyrenesulphonate is doped to, pure water of 5xcx9c70 wt. % and silicon alkoxide of 1xcx9c10 wt. %.
With such methode, the organic polymeric electroconductive film coated on the outside of the image display glass plate contains polyethylenedioxythiophene which polystyrenesulphonate is doped to, which is simply formed without any damage during its coating process and has excellent electroconductivity and antireflection.